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Mixing Bias and Radial tires?

Discussion in 'Motorcycle Talk' started by MB2, Apr 2, 2011.

  1. So lets say you decided to run a Radial front tire and a Bias-ply rear, what sort of handling characteristics should you expect?

    That is, I realize it's bad to mix the two...but under what specific situations would it be noticed?

    Lets say for example you did that and you noticed the following, would these likely be caused by the tires?
    -In the rain the rear feels like it breaks loose on corners and wants to drift a little.
    -On dry/clean pavement when leaning/riding aggressively the bike 'skips' and bounces up and down (maybe 3-5 times) quickly at the apex.

    Thoughts? First hand experience?
  2. Both of those examples and pretty much any other time you are riding.
    It's freaky in a car, but downright dangerous on a bike.
    Get the right tires or park te bike until you can.

  3. Jims08Z06

    Jims08Z06 Bat Crazed

    oh no :scared:scared:scared:scared:scared:scared:scared
  4. DON'T YOU'LL BE SORRY. I agree with jims08z06 :scared :scared
    Last edited: Apr 2, 2011
  5. Oh no.....

    Never mix 'em. It may be ok to upgrade to radials, but the difference between the two tire types is signifigant enough that the characteristics of the tires can throw your bike's handling waaaay off. If it came with radials, keep 'em on there....
  6. Welp, sometimes you just find out the hard way.

    Thanks for the advice everyone, however now I'm interested in the physical reason as to why it could be an issue? I realize they are different compounds and will grip differently, but maybe I'm missing something seems under SOME conditions (even when pushing it, at a fun yet controlled speed on a corner) they should still hold up "well enough."

    Google must be failing me tonight.

    With that said, lets say you were turning aggressively for a solid half hour-hour in a parking lot at 20mph-ish (tight, and repetitively) and had no noticeable issues. Then an hour later had a higher speed, likely tire related issue?
  7. james1300

    james1300 Track School Dazed

    The Physical design of the two different tires is why its 'not safe' to use the two types on the same bike. Tire cases are differant. Rubber compounds are different. Each tire handles different in the rain. The tire wear will be different. Causing uneven tire wear and, poor handling. Especially if you really need traction in an accident avoidance situation. The 'mis-matched' tires won't work together.
    Why would you consider running 'mis-matched' tires on a motorcycle?
  8. The difference between radial- and bias-ply tires lays in the way the belt layers are set within the molds when the tires are cast. Radial tires have the primary belts set at approx. 90 degrees to the direction of rotation. When a load is put on the tire, the belts channel the deflection forces more or less directly from the contact point, through the sidewall, to the rim. This results in a contact patch which is relatively supple and can change shape readily to maintain optimum traction.

    Bias-ply tires, on the other hand, have the primary belts layered at an angle to the direction of rotation. This results in a stiffer carcass form which retains it's shape better, but any deflection forces are channeled through the belting in such a way that it results in minor deflection of the carcass at points away from the contact patch.

    Radial tires provide greatly improved traction and ride when compared to Bias-ply. I would expec if they were mixed, the difference would become apparent as speeds increased. As loads increase on the tires, the radial tire would maintain fairly consistent grip, while the bias-ply would start to feel increasingly "greasy", losing traction in a gradual manner which would make handling unpredictable as speeds varied.

    Short answer: bad idea.

    As far as hydroplaning and wet traction, that is more dependent on tread design and specific rubber compounds used than carcass construction.

    If you want to see the difference in how tires react at the limit, find videos of some roadracing in the '60s and '70s, when tires were predominantly bias-ply construction, and take note of the way the cars corner: sideways. Then find a video of a modern-day vintage race event for muscle cars or such. Same types of vehicles, the difference is that they are typically fitted with radial tires now (albeit with better tread compounding as well). I think you'll find speeds higher and handling much more composed on the same cars running modern radials.
    Last edited: Apr 3, 2011
  9. Here's first hand experience.

    Front radial, bias-ply rear, just like your setup.

    First, some background. I ride fairly agressively, even on my fat-ass PC800. The PC has wide rims, capable of accepting radial tires and requires low profile bias ply tires. In fact the bias plies are the recommended fitment. However, most bikes that are designed for bias ply tires have narrow rims that will not work well with radials of the same size/profile as the recommended bias ply tire because the radials are designed for a wider rim and mounting them on a narrower rim changes their mounted profile and contact patch area and greatly affects handling. Usually negatively.

    Back to the question at hand.

    I experienced, just as you, a feeling of looseness at the rear, especially in the wet, and chattering on harder cornering. This is because the design of a radial tire allows for a more compliant contact patch and also for a lighter construction of the tire. This means that your suspension can hold the tire on the road surface better and the contact patch stays more consistant in shape and size, both contributing to better traction. The bias-ply tire is heavier and less compliant and looses traction earlier in the same set of environmental circumstances. Hence the looseness felt at the rear. In my case it wasn't so much a hinderance as an annoyance.

    I would not mix bias ply and radial tires on a bike designed for radials simply because the bias ply tire of the correct size would not fit on the wider rims designed for radial tires.

    I would, have, and might again mix radials and bias plies on a bike designed for bias plies ONLY if the rim width is adequate for a radial tire of the proper size and ONLY radial front, bias ply rear. I don't think it would be any fun at all having your sticky rear tire push your less compliant front into chattering or a front end slide.
  10. PeteN95

    PeteN95 Moderator Staff Member

    I have been called cheap and would not dispute this. But I don't even like running different brands front to rear, let alone different types of construction!?! I would rather have a matched set of the cheapest tires, instead of a mismatched set of sticky sport tires. Motorcycle tires have to deal with many more traction angles than a car tire. A cars tires are always at about the same angle to the ground, while a bikes tires can vary over 100 degrees of angle with respect to the ground plane. The shape, stiffness, construction, materials, and specific size can all change the way the tire reacts braking, turning, or acceleration and it can be different for each at each different lean angle. Mismatched tires can create a bad conbination in a certain situation, lean, speed, surface, accel/deccel, that can be discovered at the wrong time. And even matching tires of different brand can vary in size, shape, stiffness, grip, etc.
  11. Personal expieriance: when I lived in Paso Robles, CA. we went to American West Tires. the losers put 2 radials on the front of an old Scout 4x4 that had bias's on the rear (and bias that they took off to replace with radials) the rig darted back and forth on the road and became unsafe to drive. I found this thread and was talking to my mother about it. Eather those guys are truely the dumbest tire guys on earth, or they were gambling with our lives that we'd obviously be back (If we lived!) to buy 2 more radials. I didn't know what was wrong back then, but later I was reading the DMV manual for beggining drivers and it even says right there for new drivers to check their vehicle, make sure not to mix radial and bias on the same vehicle!!!!!!!!!!!!! How could ANY tire store screw up that bad!?!?
    Last edited: Apr 3, 2011
  12. Mount up some good knobbies and you're good to go :mrgreen:

  13. Hmm... Ya know I have enough difficulties with faith in my traction to purposely introduce known problems. I ride in all kinds of weather and just can't afford to not have confidence that my tires are going to stick to the road. This doesn't make sense to me.
  14. While this is not the optimal thing to do for any vehicle, it is not the end of the world if you do it. Unless you are pushing the bike to the limits or riding it harder than most, you wont notice much of a real difference in performance at normal riding speeds.

    Firstly, skipping and bouncing is not always a problem with tire traction but suspension. Your particular bike is not going to be breaking it loose under power or under normal riding conditions. Hops and skips are caused by the bikes suspension not being able to keep the tires firmly planted to the ground.

    Any quality tire put on a GS500 is going to provide way more traction than you need. Where you are going to notice a difference between having mis matched tires is not at low speed but at high speed. Just tooling around on it is not going to give you any issues. Riding aggressively and pushing the tires then you will notice a difference. More importantly is the condition of the tires. If you have one that is fresh like your rear and one that is worn a bit like your front, that is more likely to cause odd handling than the differences in two tire types.

    For what it is worth, I have ridden many bikes with mixed tires. Its not uber dangerous, they don't handle at optimal performance but they wont make a bit of difference at low speeds in normal riding conditions for a lot of people.
    Another thing you should note that some Harley Davidson products come with radial wide rears and bia ply fronts so the practice of doing this is not as dangerous as PNW would like you to think;)

    If it you plan on riding this bike a bit faster, I would go ahead an stick the matching Bias ply front on your machine as there is no radial sizes to be had in 130/70/17 rear and it is what came on your machine in the first place. Your front size is avail in both bias and radial but it originally came with bias ply tires.
  15. I ran a Bias ply on the front and a Radial Car tire on the rear for 19,000 miles with no ill effects, to include panic stopping in the rain. The rear Car tire had so much more grip than the OEM motorcycle rear tire and I could push the front tire out anytime I wanted to in a corner.

    But I would not think of running a Radial on front and Bias on the rear.

    If you are haveing a problem finding a Correct size Bias front tire for the front, see if you can find a rear tire in the correct size, and run it mounted backwards.
  16. Thanks for the info, Driftertank, that was exactly what I was looking for - information wise. Thanks everyone else for the opinions, and experience.

    Adrian (bubba_zenetti), I don't disagree with what you are saying overall. However I would disagree that what I experienced was likely suspension related. I realize it's tough to explain a specific situation in ways everyone can fully understand, but from what I know in advanced bicycle suspension I would not relate what I felt to how my suspension reacts. Although, I will say that I CAN push the tire combination a reasonable amount and they perform better than I believe people are giving them credit for...but you have to prepared for a performance change when riding them - which could become an issue in my opinion.

    For what it's worth, I've made up my mind based on the information provided and what I've experienced. Adrian, if you can come up with ANY radials for the rear (130/70 or 140/70 flavor) that you can get for me I'd love to hear about them. I've found several radials that I believe will suite my needs on the interwebs, but of course I'd rather support your local business if I can.
  17. Bridgestone makes a 130 radial for your bike and the ninja 250. As far as I know, it is the only radial tire made in a 130/70/17. Traction wise it is not any better than a bias ply BT45. For the $$ the BT45s are a better value.
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